The ecology of host-microbiota associations in sharks.

Abstract

The health and function of most multicellular eukaryotes is underpinned by innate associations with microorganisms. Understanding the interactions between eukaryotic hosts and their microbiota is particularly important for apex predators such as sharks, as disruptions to such interactions can cascade through entire ecosystems. Shark populations are declining globally, yet many aspects of their physiology and life history, including their microbial ecology, are still poorly understood. This study used 16S rRNA gene amplicon sequencing to characterise the microbial landscape of shark species in eastern Australia. Relationships between endogenous (species, body region, sex) and exogenous (habitat, time, epibiosis) factors and the structure of bacterial communities associated with sharks were assessed. There was strong variation between shark body regions, as well as hostspecificity of the bacterial community structures in White (Carcharodon carcharias), Bull (Carcharhinus leucas), Dusky Whaler (Carcharhinus obscurus) and Port Jackson (Heterodontus portusjacksoni) sharks. Temporal sampling of Bull and Port Jackson sharks found consistencies in the specificity of bacterial communities within body regions over time. In Port Jackson sharks, life stage and sex were found to be significant factors structuring bacterial communities associated with certain body regions, and the presence of leeches (epibionts) was correlated with structural shifts in the shark-associated bacterial communities. Broader assessment of shark epibionts in White, Tiger (Galeocerdo cuvier) and Port Jackson sharks identified novel epibiont records and hypersymbiosis. This study increases our understanding of the microbial ecology of sharks and highlights the value of studying the microbial and invertebrate taxa present within the shark landscape, given their potential roles in the health and function of vertebrate hosts.